This paper is organized as follows. In Sec. II we discuss the role of entanglement in the Grover's algorithm. In Sec. III we compute the three-tangle[1]} of some rank-2 mixture. The result of this section will be
used in Sec. V. In Sec. IV we briefly review the HHL algorithm. In Sec. V we compute the tripartite entanglement at every steps of the HHL algorithm. In Sec. VI a conclusion and further discussion are presented.
In appendix A the quantum phase estimation (QPE) is discussed when the unitary operator \(U\)  is operated to the non-eigenvector \(\vert \psi  \rangle \) . The result of this appendix is used in Sec. IV.
